Piezoelectric device



8, 1939. c. E. SEMPLE, JR 2,168,@

PIEZOELECTRIC DEVICE Filed Aug. 5, 1935 INVENTOR.

ATTORNEY.

Patented Aug. 8, i939 2,168,809 F rmzoamo'rnro pnvroa Charles E. Sample, Jrn, Youngstown, Ohio Application August 5, 1935, Serial No. 34,658 12 Claims. (01. 179-110) This invention relates to the art of piezoelectric devices, and contemplates the use of a so-called bimorph crystal element.

As is well-known, a "bimorph element consists of two crystals cemented together in such manner that one of the crystals contracts whilethe other expands when subjected to voltage. The crystals of such an element may be oriented .in such manner that two diagonal corners of a crystal will turn down while the other two corners turn up when a voltage is applied. Conversely, the same element may be utilized to produce a voltage by the application of mechanical pressure to the element, as will be readily understood. My device may be employed either as a speaker or microphone.

The present invention in its broad aspect contemplates the use of either a "torque crystal element or a bender crystal element.

More specifically, this invention embodies a single bimorph element and a pair of diaphragms co-ordinated therewith in such manner as to produce highly desirable results with respect to both quality and out-put. This particular combination constitutes one object of my invention, and is a'great improvement upon prior high grade devices in which there have been employed two crystals so arranged that the sound waves would impinge directly upon the crystals when employed, for instance, as a microphone. The possibility of using only one bimorph crystal, accordingly, constitutes an important object of the present invention.

Another object is to devise such a unit that can be produced at a very low cost.

A still further object is to devise such a unit that can be made of comparatively small size,

while still possessing extremely high efficiency, so. that it willbe readilyadaptable to uses and with advantages, either singly or in multiple, heretofore impossible.

Other objects willappear from the following description and claims when considered together with the accompanying drawing.

Referring to the drawing,

Fig. '1 is a perspective view of a bimorph" Rochelle salt crystal element in which the two crystals are cemented together in such manner as to function as a torque element;

Fig. 2 is a perspective of one of the duplicate yokes employed for fastening the crystal to the diaphragms;

Fig. 3 is a perspective of one of the duplicate diaphragms;

Fig. 4 is a perspective of the housing member or support; and

Fig. 5 is a perspective view, broken away, illus-, trating the complete assembly of a microphone embodying my invention.

Referring now to the drawing in detail, the

' "bimorph'f crystal element l is mounted centrally within the medial plane of the housing member 2, which may be made of Bakelite or other suitable material, and is arranged between the oppositely 10 disposed duplicate, conical diaphragms 8. In the present illustration, it will be observed that the crystal element is of substantially square form with the four corners thereof squared off so as to facilitate engagement of the crystal element 15 at these four points with the slots 6 of the duplicate, substantially semi-circular, yoke members 5. Suitable adhesive ,material may be employed at these points of engagement between the yoke members and the crystal element, so as to render '20 the same more secure. These yoke members are formed as metal stampings and are arranged in planes at right angles to each other, with their.

projecting ears 6 extending out through the centrally disposed apertures 3 of the diaphragms 3. 5 The engagement of the ears 6 in the apertures 3 can be rendered more secure, if so desired, by means of solder at these points.

The outer marginal portions of the diaphragms 3 are reinforced by means of an annular groove 30 3 which is formed therein in the operation of stamping out the diaphragms which are made of suitable light weight flexible metal. The edge portions of the diaphragms are secured to the opposite sides of the annular housing member 2 35 by means of adhesive material or in any other suitable manner.

.vided in the usual manner as desired.

It will be observed that in the present form of device, the same single bimorph element co-operates with the two diaphragms, the structure and arrangement of these parts being such that there 45 is produced a double form of unitary device which is capable of greatly. increased work. Hence there is obtained a greatly amplified effect with a single bimorph element.

When this device is used as a microphone, the 50 sound waves will be impinged against both diaphragms 3 which will transmit their vibrations to the crystal element i, the movements of one diaphragm causing corresponding movement of two diagonally opposite corner portions of the crystal 55 cut improved device.

stantlally.

element in the direction opposite to that in which the other diagonally opposite corner portions oi the crystal element are simultaneously the other diaphragm.

In carrying out my invention, diilerent types of crystal elements may be employed, either "bender or "torque", all of which modifications include a of oppositely disposed diaphragms, whereby it-is possible to obtain a greatly heightened eifect, whether. the device be employed as a microphone or speaker. and likewise it is possible to produce ,a given desired eifect" with a device of considerably smaller proportions than has heretofore been possible. Likewise, in constructing a multiple unit assembly for a given capacity. my invention makes it possible to use fewer units than heretofore required. These advantages may be realized without any serious sacrifice in quality, the unit embodying my invention being capable of high fidelity in frequency response.

Because of the manner in which all possible eifect of the crystal element is here utilized, 1 am" able to produce maximum work in such a device. The structure and arrangementof the several parts, includingthe diaphragms and yoke members. makes it possible to obtain such a heightened eilect with but a single crystal element. Furthermore, the structure involved is extremely simple and compact and the parts are of duplicate form. At the same time, the structure is readily assembled, it isof balanced form and arrangement and is extremely dependable and very eiileient both in quantity and quality of work.

In this construction, the crystal eiement'might be considered as a floating element suspended between the diaphragms by means of the yoke members. And the effects produced upon the two sides of the crystal element. are so co-ordinated by virtue of .theparticular connections provided, that there is obtained a greatly amplifled result which is more than that to be expected from the combined eflect of two devices of the ordinary single form and of this same size. Thus, the co-ordination of the oppositely disposed diaphragmsand the single centrally disposed crystal element, lends an unexpected and unaccountable additional amplification in the work performed.

The'great saving in cost of manufacture constitutes another important advantage of my pres- Whi le thediaphragms, fre hereyshown of conical iorm, other forms may be, employed. Also, the fsjllt shqwn here as being of sub- I x shapegmay be .of other shapes. Likewisaother details 'of my structure might be varied without departing mm the spirit of my invention as'hereiniset forth and .claimed.

WhatIclaimis:

. l. A piezo-electric'devioe comprising a single "bimorp crystal element of polygonal slab I iorm, diaphragms arranged upon opposite sides the crystal element, and operative means 0! connection between said crystal element and said diaphragms, said meansof connection being applied to individual pairs of diametrically opposite points of said cr'ystal element.

2. A piano-electric device comprising a single "bimorph" crystal element of polygonal slab iorm, diaphragms arranged upon oppoflte sides 'of the crystal element.-and operative means of connectionbetween said crystal element and said diaphragms, said means of connection being applied to individual pairs of. diametrically oppo- D amaaoo site points of said crystal element, said means of connection on opposite sides of said nection being applied to individual pairs of opposite portions of said crystal elements.

4. A piezo-electric device comprising a single "bimorph" crystal element of substantially rectangular slab form, diaphragms arranged upon opposite sides ofthecrystal element. and operative means of connection between said crystal element and said diaphragms, said means of connection being applied to individual pairs of diagonally opposite corner portions of said crystal elements.

5. A piezo-electric device comprising a single torque "bimorph crystal element of substantially square slab form, diaphragms arrangedv upon opposite sides oi the crystal element, and operative means of connection between said crystal element and said diaphragms, said means of connection being applied to pairs of diagonally opposite corner portions of said crystal element.

6. A piezo-electric device comprising a housing ring member, duplicate conical diaphragms arranged upon and secured to opposite sides of said ring member, a single bimorph crystal element of substantially square slab form arranged in the medial plane of said ring member, and duplicate substantially semi-circular yoke members each providing operative connection between one of saiddiaphragms and diagonally opposite corner portions of said crystal element. 7

7. A piezo-electric device comprising a single .bimorph crystal element, duplicate diaphragms arranged upon opposite sides of the crystal element, and duplicate operative means of connection between said crystal element and said diatrally' connected to two opposite points of said crystalelement, and the basal planes of said diaphragmsand that of said crystal element being substantially parallel. L

Q-. piezo-electrlc device comprising a single bimorphcrys'tal element of polygonal slab form, diaphragms arranged upon opposite sides of the crystal element, and operative means of connection between said diaphragms and crystal element, the basal planes of said diaphragms and crystal element being substantially parallel, and said crystal element being supported solely by said means of connection.

10. Apiezo-electric device comprising an open form of housing member, diaphragms arranged upon and secured to opposite sides of said housing member, a single floating bimorph crystal element, the basal planes of said diaphragms and crystal element being substantially parallel.

11. In a piezo-electric cell, a pair of diaphragms, a piezo-electric crystal entirely supported from and between the diaphragms, the supporting means having a pair of supporting members extending from opposite points adjacent the periphery of the crystal, said supporting means being operably connected to one diaphragm, and a second supporting means having a pair of supporting members extending from opposite points adjacent the periphery of the crystal, said second supporting means being operably connected to the other diaphragm.

12. In combination, a single piezo-elec'tric crystal, means responsive to sound waves, a floating connection between said crystal and sound-responsive means and comprising means for supporting the crystal at two points thereof on the sound-responsive means, and means operatively engaged to the sound-responsive means and to the crystal at a third point not in line with the first two points whereby sound waves cause torslonal movement of the crystal.

CHARLES E. SEMPLE, JR. 

